There is well known a type of electric toothbrush in which a brush moving at high speed abut on teeth to perform brushing of teeth (remove a food residue or dental plaque). In such electric toothbrushes, an obtained cleaning effect depends on an angle at which the brush abuts on the teeth. For example, when the brush abuts on a tooth axis at 90 degrees, the highest dental plaque removing force can be exerted with respect to a tooth plane. When the brush abuts on the tooth axis at 45 degrees, a tip of brush invades easily into an interdentium or a periodontal pocket (between tooth and gum-ridge), and the food residue or the dental plaque can effectively be scraped out from the interdentium or the periodontal pocket.
Thus, there is an optimum brush angle (angle of the brush with respect to the tooth axis) according to a brushing region or the desired cleaning effect. However, few users are conscious of the desired brush angle. Even if the user is conscious of the brush angle, because the user cannot confirm a state in which the brush abuts actually on the teeth during the brushing of teeth, the brush angle is hardly matched with the optimum value.
For example, Patent Document 1 discloses an idea in which an orientation of the toothbrush main body about an axis is detected at four or eight stages to estimate the brushing region from the detection result. Specifically, a plurality of fan-like partitions are circumferentially provided in the main body, and which partition a conductive sphere is in is detected from a change in electric resistance, thereby estimating the orientation of the toothbrush main body. However, the mechanism disclosed in Patent Document 1 is hardly miniaturized and implemented.